The present invention relates to a protective coating composition for dual damascene process or, more particularly, relates to a coating composition to form a protective coating film on a finely patterned resist layer used in the dual damascene process, which is capable of planarizing a patterned resist surface having a level difference between areas with a densely crowded pattern and areas with an isolated pattern.
In connection with semiconductor silicon-based integrated circuits, use of copper as a wiring material is under studies in recent years to provide a solution for the problems due to wiring resistance or wiring delay. In place of the conventional prior art method for the formation of wiring in an electronic device by etching of a thin metal film, the so-called dual damascene process is also highlighted, in which wiring of a metallic material is formed by implanting the material by plating. When formation of a via hole is followed by the formation of a trench hole by this dual damascene process, it sometimes occurs that the wiring material provided in advance on the substrate surface is damaged during formation of the trench after formation of the hole so that such damage is prevented by forming a protective film within the hole. The requirements for this protective film include the antireflection characteristic to reduce reflection of the exposure light on the substrate surface, implanting characteristic for complete filling of the hole not to leave an unfilled space and planarizing characteristic to keep constancy of the substrate thickness after implantation.
While the material for forming the protective film is usually an organic material such as a photoresist composition suitable for development with an alkaline developer solution (Japanese Patent Kokai 10-223755), such an organic material is disadvantageous because, when the hole has a relatively large aspect ratio, a bubble or void is formed in the course of the baking treatment within the hole to decrease the protecting effect on the metallic material and, in addition, when a protective coating film is formed by coating the substrate surface having a densely patterned area (referred to as the Dense area hereinafter) and isolatedly patterned area (referred to as the Iso area hereinafter) as is illustrated in FIG. 1, the film thickness cannot be even adversely influencing the succeeding trench-forming step by the photolithographic process.
The present invention accordingly has an object, in view of the above described problems in the prior art to provide a coating composition capable of giving a protective coating layer on a patterned resist layer having a hole pattern, which is free from occurrence of a void within the hole even when the aspect ratio of the hole is great and which has a fully planarized surface with evenness of the film thickness when the protective coating layer is formed on a patterned resist layer having both of Dense areas and Iso areas.
Thus, the present invention provides a protective coating composition for a dual damascene process comprising (A) a resinous ingredient and (B) a crosslinking agent dissolved in an organic solvent of which the weight proportion of the resinous ingredient as the component (A) and the crosslinking agent as the component (B) is in the range from 2:8 to 4:6 and the overall weight-average molecular weight of the solid matter, i.e. components (A) and (B), is in the range from 1300 to 4500.